1. Field of the Invention
The present invention relates to a bag forming/filling system wherein a web from a web roll is allowed to hang down while being formed around a bag forming cylinder into a tubular shape by intermittent operation of a delivery portion, or mechanism which is located at an opposed position to an outer surface of the bag forming cylinder. The web is then sealed in a transverse direction by a closing motion of a transverse sealing machine to form a bag. The interior of the bag is then filled with material to be packed.
2. Description of Background and Relevant Information
A known bag forming/filling system is disclosed, for example, in Japanese Patent Laid-Open Application No. 158630/87. According to this conventional bag forming/filling system, a predelivery mechanism, which includes a predelivery roller and a tension lever, is pivotally positioned on a downstream side of the predelivery roller in a delivery path extending from a web roll up to a bag forming cylinder. A web is passed onto both of a plurality of rotatable tension rollers which are journalled to the tension lever and onto a plurality of guide rollers disposed in an opposed relation to those tension rollers, so that constant tension is applied to the web by the weight of the tension lever and the tension rollers. Furthermore, two delivery belts, which act as delivery portions, are disposed on the outer peripheral portions and on both opposed sides of the bag forming cylinder so as to be in abutment with both transverse side portions of the web. Both delivery belts are adapted to perform an intermittent operation, whereby the web is delivered intermittently by a predetermined length at a time. Pivotal movement of the tension lever is detected by a detector and the predelivery roller is rotated, whereby the web is pulled out from the web roll and the tension lever is brought back into its initial position, so that the force of pulling out the web from the web roll is diminished and the web is kept under tension.
In such a known bag forming/filling system, however, since the web is delivered intermittently by the delivery portions while being kept under constant tension, the delivery resistance of the web is high, and unless the delivery force of each delivery portion is large, it is impossible to ensure the intermittent delivery of the web, thus resulting in increase of the cost. In the event a force is generated which is in a transverse direction relative to the delivery direction of the web being delivered, for example due to a defective setting of the web roll or a dimensional error of the web itself, a positional deviation of the web will occur, and the web will easily move over side guides which project therefrom with the result that the product obtained is defective.
The two delivery belts operate at the same speed to intermittently deliver both transverse side portions of the web by the same length at a time. If a difference in frictional resistance occurs between both delivery belts, which are in abutment with both transverse side portions of the web, due to a minor problem (for example, a surface stain on one delivery belt or the difference in quality between the two belts), one delivery belt will slip with respect to one side portion of the web. Accordingly, the other side portion of the web is forcibly pulled by only the other deliver belt, resulting in the web being skewed in the transverse direction, and the delivery resistance of the other web side portion being forcibly delivered increases, so that the other delivery belt, which is in abutment therewith easily slips. Repetition of such slippage results in meandering of the web and defective products.
To lower the occurrence of such defects stopping the operation and re-adjustment at every start of the transverse movement of the web are required, but this is not only troublesome but also lowers the operating efficiency.
Further, since it is necessary to provide a drive source for the predelivery mechanism which is separate from the drive source for the delivery belts and the transverse sealing machine, the structure is complicated and the cost becomes high.